Many ground-based navigation applications require directional knowledge. Examples of such applications include aiming/targeting techniques (e.g., for mortar/artillery), navigation of autonomous ground vehicles, and surveying techniques. An important piece of information for use in ground-based navigation is knowledge of one's direction relative to the desired path of travel along the surface of the earth.
Conventional techniques for obtaining directional knowledge include using magnetic compasses, the Global Positioning System (GPS), gyroscopes, and radio signals. These techniques all present certain disadvantages. Magnetic compasses require local calibrations to obtain even marginal accuracy. The GPS requires supporting electronics and cannot be used underground. The GPS also requires the user to be moving, or the big antenna separation is needed for achieving accuracy. Also it is susceptible to local area jamming. Conventional gyroscopes are typically too large and expensive given accuracy needs.